Oxide Semiconductor Thin‐Film Transistors: A Review of Recent Advances
TL;DR: The recent progress in n- and p-type oxide based thin-film transistors (TFT) is reviewed, with special emphasis on solution-processed andp-type, and the major milestones already achieved with this emerging and very promising technology are summarizeed.
Abstract: Transparent electronics is today one of the most advanced topics for a wide range of device applications. The key components are wide bandgap semiconductors, where oxides of different origins play an important role, not only as passive component but also as active component, similar to what is observed in conventional semiconductors like silicon. Transparent electronics has gained special attention during the last few years and is today established as one of the most promising technologies for leading the next generation of flat panel display due to its excellent electronic performance. In this paper the recent progress in n- and p-type oxide based thin-film transistors (TFT) is reviewed, with special emphasis on solution-processed and p-type, and the major milestones already achieved with this emerging and very promising technology are summarizeed. After a short introduction where the main advantages of these semiconductors are presented, as well as the industry expectations, the beautiful history of TFTs is revisited, including the main landmarks in the last 80 years, finishing by referring to some papers that have played an important role in shaping transparent electronics. Then, an overview is presented of state of the art n-type TFTs processed by physical vapour deposition methods, and finally one of the most exciting, promising, and low cost but powerful technologies is discussed: solution-processed oxide TFTs. Moreover, a more detailed focus analysis will be given concerning p-type oxide TFTs, mainly centred on two of the most promising semiconductor candidates: copper oxide and tin oxide. The most recent data related to the production of complementary metal oxide semiconductor (CMOS) devices based on n- and p-type oxide TFT is also be presented. The last topic of this review is devoted to some emerging applications, finalizing with the main conclusions. Related work that originated at CENIMAT|I3N during the last six years is included in more detail, which has led to the fabrication of high performance n- and p-type oxide transistors as well as the fabrication of CMOS devices with and on paper.
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TL;DR: In this article, the performance of InZnO thin-film transistor (TFT) using as dielectric an ultra-thin solution-processed ZrO ${x}$ layer was evaluated.
Abstract: This paper deals with the evaluation of the performances of InZnO thin-film transistor (TFT) using as dielectric an ultra-thin solution-processed ZrO $_{x}$ layer. The ZrO $_{x}$ thin film was formed using ultraviolet (UV) photo-annealing method and shows a low leakage-current density of 4 nA/cm $^{2}$ at 3.8 MV/cm and a large areal-capacitance of 775 nF/cm $^{2}$ at 50 Hz. The InZnO TFT incorporating the UV-treated ZrO $_{x}$ dielectric exhibits high stable and enhanced characteristics, an on/off current ratio of ${\hbox{10}}^{7}$ , a field-effect mobility of 14.7 cm $^{2}/{\hbox{V}}{\cdot}{\hbox{s}}$ , a subthreshold swing voltage of 100 mV/decade and a threshold voltage shift under bias stress, for 2 hours less than 0.1 V. All these performances are obtained at a low operation voltage of 2 V and make it suitable for use as a switching transistor in low-power electronics applications.
17 citations
TL;DR: In this paper, a more practical use of a-IGZO-based TFTs by adopting plasmonic fi lters (PFs) was reported, where metal structures at the submicron scale demonstrate a unique optical response known as a surface plasm (SP), which can be easily designed by the material and geometrical factors.
Abstract: wileyonlinelibrary.com gate bias stress during most of the driving time and transparent devices are exposed to ambient light unavoidably. The stability resulting from electrical stress under light illumination is important since it can deteriorate the switching performances of a-IGZO-based TFTs. It was found that the positive bias illumination stress is insignifi cant compared to the negative bias illumination stress (NBIS). [ 7 ] NBIS has been explained by photo-induced carriers and the state transition, [ 7–10 ] but the exact mechanism is under debate. In addition, previous reports to improve the stability from NBIS are still insuffi cient from a device viewpoint. Herein we report a more practical use of a-IGZO-based TFTs by adopting plasmonic fi lters (PFs). Metal structures at the submicron scale demonstrate a unique optical response known as a surface plasmon (SP). A metallic fi lm with two dimensional nanohole arrays shows high transmission at the SP resonance frequency and the optical response related to this resonance phenomenon can be easily designed by the material and geometrical factors. This structural coloring technology using thin metal fi lms is superior in fi ltering performance compared to the conventional dye-based color fi lter that experiences degradation by heat and light due to the low chemical stability of the organic-dye material. In addition, thin and quasi-planar structures are advantageous in that they can be easily integrated with other devices. Therefore, PFs have recently been highlighted for use in industrial imaging applications such as CMOS image sensors and displays. [ 11,12 ]
17 citations
TL;DR: In this article, the effects of illumination and bias illumination stresses on the electrical performance of p-type tin monoxide (SnO) thin-film transistors (TFTs) were investigated.
Abstract: We investigated the effects of illumination and bias illumination stresses on the electrical performance of p-type tin monoxide (SnO) thin-film transistors (TFTs). The transfer curve shifts in the positive direction with an increase of the subthreshold slope (SS) and OFF-current ( $I_{\mathrm {OFF}}$ ) under light illumination, where the increase in SS and $I_{\mathrm {OFF}}$ under illumination was attributed to the photoconductivity in SnO, especially at the back channel region. The positively shifted transfer curve by light illumination recovers to the initial one within 3000 s after turning OFF the light source. The trapping and detrapping of the photogenerated electrons in bulk defect states of SnO were considered as the most probable mechanism for the illumination-induced positive shift of the transfer curve and persistent photoconductivity in p-type SnO TFTs. There was no significant difference in the degree of light-induced-degradation between the TFTs with and without a passivation layer, which was mainly attributed to the weak chemisorption of oxygen molecules on SnO. Threshold voltage shift ( $\Delta V_{\mathrm {th}}$ ) is much decreased under negative bias illumination stresses than under negative bias stresses, but $\Delta V_{\mathrm {th}}$ increases under positive bias illumination stresses than under positive bias stresses in p-type SnO TFTs.
17 citations
TL;DR: In this paper, the authors employed a variety of analytical methods such as X-ray photoelectron spectroscopy (XPS), ultraviolet photo-electron (UPS), and Hall measurement to identify the main contributors to the physical properties of SnO.
Abstract: Over the past several decades, tin monoxide (SnO) has been studied extensively as a p-type thin film transistor (TFT). However, its TFT performance is still insufficient for practical use. Many studies suggested that the instability of the valence state of Sn (Sn2+/Sn4+) is a critical reason for the poor performance such as limited mobility and low on/off ratio. For SnO, the Sn 5s-O 2p hybridized state is a key component for obtaining p-type conduction. Thus, a strategy for stabilizing the SnO phase is essential. In this study, we employ a variety of analytical methods such as X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and Hall measurement to identify the main contributors to the physical properties of SnO. It is revealed that precision control of the process temperature is needed to achieve both the crystallinity and thermal stability of SnO. In other words, it would be ideal to obtain high-quality SnO thin films at low temperature. We find that atomic layer deposition (ALD) is a quite advantageous process for obtaining high-quality SnO thin films by the following two-step process: (i) growth of highly c-axis oriented SnO at the initial stage and (ii) further crystallization along the in-plane direction by a postannealing process. Consequently, we obtained a highly dense SnO thin film (film density: 6.4 g/cm3) with a high Hall mobility of ∼5 cm2/(V·s). The fabricated SnO TFTs exhibit a field-effect mobility of ∼6.0 cm2/(V·s), which is a quite high value among the SnO TFTs reported to date, with long-term stability. We believe that this study demonstrates the validity of the ALD process for SnO TFTs.
17 citations
TL;DR: In this article, the effect of dual wavelength (185 nm and 254 nm) UV irradiation time on the conductivity of a-IGZO TFTs was studied and the lowest resistivity obtained in this study is similar to that of ITO transparent electrodes and is about 2 orders of magnitude lower than the values obtained to date.
Abstract: We have developed a new technique to fabricate coplanar homojunction structure a-IGZO thin film transistors (TFTs) by adopting selective ultraviolet (UV) irradiation in the n+ source/drain regions of an a-IGZO layer through a patterned photoresist mask. In order to apply this technique for coplanar homojunction a-IGZO TFTs, we systematically studied the effect of dual wavelength (185 nm and 254 nm) UV irradiation time on the conductivity of a-IGZO films. Various materials were evaluated to find one that provided proper shielding against UV irradiation. The resistivity of the a-IGZO film drastically decreased from an as-deposited value of 2.71 × 106 Ω cm to 3.76 × 10−5 Ω cm after UV irradiation. The lowest resistivity obtained in this study is similar to that of ITO transparent electrodes and is about 2 orders of magnitude lower than the values obtained to date. Coplanar homojunction a-IGZO TFTs were successfully fabricated by introducing an optimized process that included UV irradiation through a patterned photoresist UV mask. The saturation mobility (μsat), threshold voltage (Vth), sub-threshold swing (SS), and on/off current ratio (Ion/Ioff) were measured to be 6.7 cm2 V−1 s, 7.3 V, 0.21 V per decade, and ∼109, respectively. Moreover, we showed that the UV irradiation technique provided both a low contact resistance due to the high conductivity in the source/drain region and a small channel length modulation due to non-thermal doping behavior. We believe that this UV irradiation process is a useful technique because it is simple and results in outstanding electrical properties.
17 citations
References
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TL;DR: A novel semiconducting material is proposed—namely, a transparent amorphous oxide semiconductor from the In-Ga-Zn-O system (a-IGZO)—for the active channel in transparent thin-film transistors (TTFTs), which are fabricated on polyethylene terephthalate sheets and exhibit saturation mobilities and device characteristics are stable during repetitive bending of the TTFT sheet.
Abstract: Transparent electronic devices formed on flexible substrates are expected to meet emerging technological demands where silicon-based electronics cannot provide a solution. Examples of active flexible applications include paper displays and wearable computers1. So far, mainly flexible devices based on hydrogenated amorphous silicon (a-Si:H)2,3,4,5 and organic semiconductors2,6,7,8,9,10 have been investigated. However, the performance of these devices has been insufficient for use as transistors in practical computers and current-driven organic light-emitting diode displays. Fabricating high-performance devices is challenging, owing to a trade-off between processing temperature and device performance. Here, we propose to solve this problem by using a novel semiconducting material—namely, a transparent amorphous oxide semiconductor from the In-Ga-Zn-O system (a-IGZO)—for the active channel in transparent thin-film transistors (TTFTs). The a-IGZO is deposited on polyethylene terephthalate at room temperature and exhibits Hall effect mobilities exceeding 10 cm2 V-1 s-1, which is an order of magnitude larger than for hydrogenated amorphous silicon. TTFTs fabricated on polyethylene terephthalate sheets exhibit saturation mobilities of 6–9 cm2 V-1 s-1, and device characteristics are stable during repetitive bending of the TTFT sheet.
7,301 citations
Book•
04 Jul 1990
TL;DR: In this article, the authors present a characterization of the resistivity of a two-point-versus-four-point probe in terms of the number of contacts and the amount of contacts in the probe.
Abstract: Preface to Third Edition. 1 Resistivity. 1.1 Introduction. 1.2 Two-Point Versus Four-Point Probe. 1.3 Wafer Mapping. 1.4 Resistivity Profiling. 1.5 Contactless Methods. 1.6 Conductivity Type. 1.7 Strengths and Weaknesses. Appendix 1.1 Resistivity as a Function of Doping Density. Appendix 1.2 Intrinsic Carrier Density. References. Problems. Review Questions. 2 Carrier and Doping Density. 2.1 Introduction. 2.2 Capacitance-Voltage (C-V). 2.3 Current-Voltage (I-V). 2.4 Measurement Errors and Precautions. 2.5 Hall Effect. 2.6 Optical Techniques. 2.7 Secondary Ion Mass Spectrometry (SIMS). 2.8 Rutherford Backscattering (RBS). 2.9 Lateral Profiling. 2.10 Strengths and Weaknesses. Appendix 2.1 Parallel or Series Connection? Appendix 2.2 Circuit Conversion. References. Problems. Review Questions. 3 Contact Resistance and Schottky Barriers. 3.1 Introduction. 3.2 Metal-Semiconductor Contacts. 3.3 Contact Resistance. 3.4 Measurement Techniques. 3.5 Schottky Barrier Height. 3.6 Comparison of Methods. 3.7 Strengths and Weaknesses. Appendix 3.1 Effect of Parasitic Resistance. Appendix 3.2 Alloys for Contacts to Semiconductors. References. Problems. Review Questions. 4 Series Resistance, Channel Length and Width, and Threshold Voltage. 4.1 Introduction. 4.2 PN Junction Diodes. 4.3 Schottky Barrier Diodes. 4.4 Solar Cells. 4.5 Bipolar Junction Transistors. 4.6 MOSFETS. 4.7 MESFETS and MODFETS. 4.8 Threshold Voltage. 4.9 Pseudo MOSFET. 4.10 Strengths and Weaknesses. Appendix 4.1 Schottky Diode Current-Voltage Equation. References. Problems. Review Questions. 5 Defects. 5.1 Introduction. 5.2 Generation-Recombination Statistics. 5.3 Capacitance Measurements. 5.4 Current Measurements. 5.5 Charge Measurements. 5.6 Deep-Level Transient Spectroscopy (DLTS). 5.7 Thermally Stimulated Capacitance and Current. 5.8 Positron Annihilation Spectroscopy (PAS). 5.9 Strengths and Weaknesses. Appendix 5.1 Activation Energy and Capture Cross-Section. Appendix 5.2 Time Constant Extraction. Appendix 5.3 Si and GaAs Data. References. Problems. Review Questions. 6 Oxide and Interface Trapped Charges, Oxide Thickness. 6.1 Introduction. 6.2 Fixed, Oxide Trapped, and Mobile Oxide Charge. 6.3 Interface Trapped Charge. 6.4 Oxide Thickness. 6.5 Strengths and Weaknesses. Appendix 6.1 Capacitance Measurement Techniques. Appendix 6.2 Effect of Chuck Capacitance and Leakage Current. References. Problems. Review Questions. 7 Carrier Lifetimes. 7.1 Introduction. 7.2 Recombination Lifetime/Surface Recombination Velocity. 7.3 Generation Lifetime/Surface Generation Velocity. 7.4 Recombination Lifetime-Optical Measurements. 7.5 Recombination Lifetime-Electrical Measurements. 7.6 Generation Lifetime-Electrical Measurements. 7.7 Strengths and Weaknesses. Appendix 7.1 Optical Excitation. Appendix 7.2 Electrical Excitation. References. Problems. Review Questions. 8 Mobility. 8.1 Introduction. 8.2 Conductivity Mobility. 8.3 Hall Effect and Mobility. 8.4 Magnetoresistance Mobility. 8.5 Time-of-Flight Drift Mobility. 8.6 MOSFET Mobility. 8.7 Contactless Mobility. 8.8 Strengths and Weaknesses. Appendix 8.1 Semiconductor Bulk Mobilities. Appendix 8.2 Semiconductor Surface Mobilities. Appendix 8.3 Effect of Channel Frequency Response. Appendix 8.4 Effect of Interface Trapped Charge. References. Problems. Review Questions. 9 Charge-based and Probe Characterization. 9.1 Introduction. 9.2 Background. 9.3 Surface Charging. 9.4 The Kelvin Probe. 9.5 Applications. 9.6 Scanning Probe Microscopy (SPM). 9.7 Strengths and Weaknesses. References. Problems. Review Questions. 10 Optical Characterization. 10.1 Introduction. 10.2 Optical Microscopy. 10.3 Ellipsometry. 10.4 Transmission. 10.5 Reflection. 10.6 Light Scattering. 10.7 Modulation Spectroscopy. 10.8 Line Width. 10.9 Photoluminescence (PL). 10.10 Raman Spectroscopy. 10.11 Strengths and Weaknesses. Appendix 10.1 Transmission Equations. Appendix 10.2 Absorption Coefficients and Refractive Indices for Selected Semiconductors. References. Problems. Review Questions. 11 Chemical and Physical Characterization. 11.1 Introduction. 11.2 Electron Beam Techniques. 11.3 Ion Beam Techniques. 11.4 X-Ray and Gamma-Ray Techniques. 11.5 Strengths and Weaknesses. Appendix 11.1 Selected Features of Some Analytical Techniques. References. Problems. Review Questions. 12 Reliability and Failure Analysis. 12.1 Introduction. 12.2 Failure Times and Acceleration Factors. 12.3 Distribution Functions. 12.4 Reliability Concerns. 12.5 Failure Analysis Characterization Techniques. 12.6 Strengths and Weaknesses. Appendix 12.1 Gate Currents. References. Problems. Review Questions. Appendix 1 List of Symbols. Appendix 2 Abbreviations and Acronyms. Index.
6,573 citations
TL;DR: In this paper, a review of the literature in the area of alternate gate dielectrics is given, based on reported results and fundamental considerations, the pseudobinary materials systems offer large flexibility and show the most promise toward success.
Abstract: Many materials systems are currently under consideration as potential replacements for SiO2 as the gate dielectric material for sub-0.1 μm complementary metal–oxide–semiconductor (CMOS) technology. A systematic consideration of the required properties of gate dielectrics indicates that the key guidelines for selecting an alternative gate dielectric are (a) permittivity, band gap, and band alignment to silicon, (b) thermodynamic stability, (c) film morphology, (d) interface quality, (e) compatibility with the current or expected materials to be used in processing for CMOS devices, (f) process compatibility, and (g) reliability. Many dielectrics appear favorable in some of these areas, but very few materials are promising with respect to all of these guidelines. A review of current work and literature in the area of alternate gate dielectrics is given. Based on reported results and fundamental considerations, the pseudobinary materials systems offer large flexibility and show the most promise toward success...
5,711 citations
IBM1
TL;DR: In this article, the authors present new insight into conduction mechanisms and performance characteristics, as well as opportunities for modeling properties of organic thin-film transistors (OTFTs) and discuss progress in the growing field of n-type OTFTs.
Abstract: Organic thin-film transistors (OTFTs) have lived to see great improvements in recent years. This review presents new insight into conduction mechanisms and performance characteristics, as well as opportunities for modeling properties of OTFTs. The shifted focus in research from novel chemical structures to fabrication technologies that optimize morphology and structural order is underscored by chapters on vacuum-deposited and solution-processed organic semiconducting films. Finally, progress in the growing field of the n-type OTFTs is discussed in ample detail. The Figure, showing a pentacene film edge on SiO2, illustrates the morphology issue.
4,804 citations
TL;DR: An outlook is presented on what will be required to drive this young photovoltaic technology towards the next major milestone, a 10% power conversion efficiency, considered by many to represent the efficiency at which OPV can be adopted in wide-spread applications.
Abstract: Solution-processed bulk-heterojunction solar cells have gained serious attention during the last few years and are becoming established as one of the future photovoltaic technologies for low-cost power production. This article reviews the highlights of the last few years, and summarizes today's state-of-the-art performance. An outlook is given on relevant future materials and technologies that have the potential to guide this young photovoltaic technology towards the magic 10% regime. A cost model supplements the technical discussions, with practical aspects any photovoltaic technology needs to fulfil, and answers to the question as to whether low module costs can compensate lower lifetimes and performances.
3,084 citations